Television device



Sept. 29, 1942. A. RAPPOLD 2,297,500

TELEVISION DEVICE Filed Sept. 6, 1940 Patented Sept. 29, 1942 2,297,500 TELEVISION DEVICE Armin Rappold, Berlin, Germany; vested in the Alien Property Custodian Application September 6, 1940, Serial No. 355,565 In Germany October 26, 1939 2 Claims. (Cl. 1787.2)

When scanning a picture projected on the mosaic screen of a picture 'tube then on the receiving side of the television system a modulation is perceived in addition to the modulation which arrives from the picture under scansion. Such additional wrong modulation, spoken of as disturbing signal, is independent of the proper modulation and is uniformly distributed across the picture. During a line or picture period the disturbing signal approximately varies as represented by the curves shown in Figs. la and 11).

Two prior methods, fundamentally ditlerent from each other, aim to compensate the disturbing signal. One of them consists in electrically simulating the curves, illustrated in Figs. 1a and 1b, of the lineor picture-frequency, namely, by

superimposing on a saw-tooth of lineor picture- 1 frequency, respectively, a sine of the same frequency and a sine of double the frequency. All the values here concerned must be adjustable as regards amplitude and phase. .The modulation by which the disturbing signal is simulated in this Way is subtracted from the mixture arriving from the scanning device. As a result, with correct adjustment of all the twelve variables the disturbing signal will be compensated.

The second method consists in producing a predetermined voltage for each range of the picture by means of an auxiliary voltage source, such as a cathode ray tube of the kind having a multi-anode for secondary emission. Also in this case the curve of this voltage is simulated to that of the disturbing signal, whereby the disturbing signal may likewise be compensated by subtraction.

According to the present invention one or more cathode ray tubes serving as scanning devices, a diaphragm for each such tube and a photo-electric cell are used for producing the compensation voltage.

In the drawing, Figs. 1a, 1b is a graph already referred to in explaining the aforesaid prior methods and the main feature of the invention, Fig. 2 is a diagram showing one embodiment of the invention, Fig. 3a is a diagrammatic detail view illustrating the construction of diaphragms forming part of the arrangement represented in Fig. 2, while Fig. 3b is a graph which in conjunction with Fig. 31: serves to explain the function of such diaphragms.

The arrangement illustrated in Fig. 2 comprises two cathode ray tubes R1, R2, arranged to act as dissectors, and a photo-electric cell P. The two cathode rays are deflected in only one direcphragms each form a slot of varying width, as

will be understood from Fig. 3a. The diameter of the spot on the screens of R1, R2 is larger than the maximum width of the slot, as is illustrated by the circle in Fig. 3a. The hatched part of this circle indicates the quantity of light passing tion proportionately and synchronously with the through the diaphragm. It will be seen that at each instant of time another quantity of light will pass therethrough, namely, a quantity determined by the distances a and b, the angles 81 and a. and the diameter of the spot of light. The curve in Fig. 3b represents the variation the voltage of the photo-electric cell P undergoes, and it will be seen that this curve is rounded owing to the large diameter of the spot of light. The quantities of light which pass through the diaphragms B1, B2 are summed up in the cell P. With the values a, b, 61, 62 properly adjusted the voltage at the cell P hence is a simulation of the disturbing signal.

By subtracting this simulation from the modulation arriving from the picture scanning device and which contains the disturbing signal a modulation free from the disturbing signal is obtained. Such subtraction may be efiected by means of a multi-grid tube, for instance, arranged in the customary modulation amplifier.

In order to provide for the best compensation in each case the diaphragms B1, B2 may be adjustable or exchangeable.

What is claimed is: r

1. In a television transmitter including a cathode ray transmitter tube and means for causin said cathode ray to periodically scan a picture screen and wherein a disturbing signal is introduced during said scanning which signal unevenly shades the picture, means to compensate for said disturbing signal including a compensating cathode-ray tube having means to trace on its fluorescent screen a line in synchronism with the successive line scannings of the transmitter tube, a photoelectric cell positioned to be excited by the traced line on said compensating tube, and a slotted diaphragm between the screen of said compensating tube and said photoelectric cell for controlling the production of a compensating electrical wave by said cell having a waveform corresponding to said disturbing signal.

2. In a television transmitter including a cathode ray transmitter tube and means for causing said cathode ray to scan a picture screen in lines corresponding to the vertical and horizontal components of the picture and wherein a disturbing signal is introduced therein by said scannin which signal unevenly shades the picture, means to compensate for said disturbing signal comprising a pair of cathode-ray tubes each having means to trace on its fluorescent screen a line, one cathode-ray tube tracing a line in time synchronism 10 with the "line scanning in the transmitter tube ARMIN RAPPOLD. 

